THERMOMECHANICAL ANALYSIS OF HAIR 367

368 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Formaldehyde is highly reactive with many of the functional groups on the peptide backbone and is able to react with groups containing ac- tive hydrogens on separate polypeptide chains such that methylene bridges (crosslinks) are formed between the chains (8). The 20øC shift upscale in the transition temperatures in all three thermal analysis sys- tems is indicative of the structural role these crosslinks play in hair. The TG analysis indicates a 9% increase in the weight loss due to loosely bound formaldehyde which correlates well with the 12% increase re- ported by Reddie and Nicholls (9) for wool. The process of supercontraction causes a longitudinal shortening ot5 the sample (10-30%) and is apparently due to a further folding of the polypeptide chains into a shorter configuration. The supercontracted samples behaved somewhat like the crosslinked samples in that some of the thermal transitions were shifted upscale indicating a further stabi- lized structure. The increase in the first longitudinal contraction from 0.6 to 3% was a significant difference from control. The supercontracted hair showed no X-ray diffraction pattern, low birefrigence, and an in- crease in diameter of 100%. These alterations, including those observed in the thermal analysis, were reversible following 24 hours' soaking in water. Hair which had undergone supercontraction did not have the prop- erties of the original a-keratin or that of a completely fi-structured system (e.g., silk), since silk has a distinct X-ray pattern and significantly different thermal properties (6). Oxidation with hydrogen peroxide results in an increase in the tran- sition temperature similar to those effected by supercontraction. An in- crease in transition temperature following bleaching was observed by Deem and Rieger (10) from stress-strain analysis. The authors report a 10øC increase in a second-order phase transition in hair after bleaching. In the TMA, the H202oxidized hair exhibited a greater degree of softening in the lower temperature range (60ø C) and a reduced expansion at 276øC. The use of performic acid further emphasized the effects ob- served with H202. The transition temperatures were shifted 40øC and the expansion was reduced to 3%. Felix et al. (11) report for wool that after 50 min in performic acid, the 220-230øC endotherm is absent. The data from the present study could also be interpreted in that way. The first being absent, the second is slightly shifted upscale (14øC) and a new endotherm at 297øC is de- veloped.